body {
    height: 1000px;
}
.big {
    width: 500px;
    height: 500px;
    border-radius: 50%;
    border: 1px dashed black;
    margin: 50px auto 0 ;
    position: relative;
    /* animation: cir1 10s; */
    animation: zhuan 7s linear infinite;
}
#sun {
    width: 200px;
    height: 200px;
    background-color: red;
    border-radius: 50%;
    position: absolute;
    top: 150px;
    left: 150px;
}
.small {
    width: 100px;
    height: 100px;
    border-radius: 50%;
    border: 1px dashed blue;
    position: absolute;
    top: 200px;
    left: -50px;
    animation: zhuan 1s linear infinite;
}
#earth {
    width: 50px;
    height: 50px;
    border-radius: 50%;
    background-color: blue;
    position: absolute;
    top: 25px;
    left: 25px;;
}
#moon {
    width: 20px;
    height: 20px;
    border-radius: 50%;
    background-color: #ccc;
    position: absolute;
    top: 40px;
    left: -10px;
}
@keyframes zhuan {
    /* form {transform:rotate(30deg);} */
    to {transform:rotate(240deg) }
}